The present invention relates to a novel multibeam electron gun and a novel method for assembling that gun. The novel gun and novel method can provide better alignment of successive grid apertures, better control of spacing between successive grid electrodes and a reduction in electron gun distortion as compared with prior gun designs.
U.S. Pat. No. 4,298,818, issued Nov. 3, 1981, describes an electron gun for use in a multibeam cathode-ray tube. The gun includes at least two spaced successive electrodes brazed directly to metallized patterns on one surface of a ceramic support and a plurality of cathode support assemblies brazed directly to metallized patterns on the opposite surface of the ceramic support. Each electrode comprises a single metal plate having three beam-defining apertures therethrough, which apertures are so aligned as to permit the passage of three electron beams. The sizes and shapes of the electron beams are determined, in part, by the sizes, shapes and alignments of the apertures. Apertures that are misaligned by as little as 0.0125 mm (0.5 mil) can cause distorted beam shapes and degrade the performance of the tube.
U.S. Pat. No. 4,500,808, issued Feb. 19, 1985, describes an improved electron gun similar to that of U.S. Pat. No. 4,298,818 except that the second electrode comprises a composite structure having a metal support plate brazed directly to a metallized pattern on one surface of a ceramic support. The metal support plate has a window therein opposite each of the apertures in a first electrode which is also brazed directly to a separate metallized pattern on the same surface of the ceramic support. Separate metal plates are brazed to the metal support plate and close the windows therein. Each of the metal plates has a single electron beam-defining aperture therein which is separately aligned with one of the apertures in the first electrode. This structure provides more accurate alignment of successive grid apertures than previous structures.
In each of the above-described electron guns, the successive electrodes and the cathode support assemblies are simultaneously brazed directly to metallized patterns formed on the ceramic support. This simultaneous brazing process has several drawbacks, some of which include: the difficulty of adjusting the spacing between successive electrodes; the difficulty of removing the completed assembly from the brazing fixture; dirt in the brazing fixture can effect alignment of the apertures; forming the electrode contact leads can change the spacing between the electrodes and, most importantly, the brazing operation frequently distorts the metal parts and imparts stress into the ceramic support which can crack the ceramic support. As a result, a structure and assembly process are required which reduce or eliminate the drawbacks of the prior art.